A polymer electrolyte can be readily processed into a thin membrane which is useful as a separator and ionic conductor in electrochemical cells. Polymer electrolyte membranes have been used in electrolysis, batteries and fuel cells. To further increase the current density and energy density in an electrochemical cell, polymer electrolyte with high ionic conductivity and ion exchange capacity is desired. Polymer electrolytes with high ion exchange capacity, however, typically suffer from poor mechanical properties, especially at high relative humidity. Some of the hydrocarbon electrolytes and perfluoropolymer electrolytes also suffer from mechanical degradation after many repeated humidity cycles leading to irrecoverable performance losses. Incorporating a reinforcing nonionic polymer into a polymer electrolyte results in lower ion exchange capacity. As the nonionic polymer is not usually compatible with a polymer electrolyte, a blend of nonionic polymer with a polymer electrolyte may have inferior mechanical properties. There is thus a need to improve the mechanical properties of a polymer electrolyte membrane without compromising its electrochemical performance.